1. Field of the Invention
The present invention generally relates to vehicle suspension systems and, more particularly, toward an independently suspended beam structure for a multi-use vehicle.
2. Description of Related Art
It is known to independently suspend wheels from a vehicle frame. An independently suspended wheel is able to move in one or more directions without affecting the movement of any other wheels. It is desirable to independently suspend wheels to improve the ride of a vehicle when traveling over a road or ground that may be uneven. It is also desirable to use a track on each side of the vehicle. The use of a track, rather than individual wheels only, improves the vehicle's flotation on soft ground as well as the traction. It is particularly important to use an independent suspension system when a track is used, to maximize the amount of surface area of each track in contact with the ground on each side of the vehicle.
It is also known to suspend beams from vehicles. In a typical configuration, a beam is suspended on each side of a vehicle. Two or more wheels are attached to the beam. Typically, axles or other structures rigidly interconnect the beams so that the beams move together relative to the frame. These types of structures are normally used in areas where the terrain is likely to be substantially level.
Some suspension systems are like those used on military vehicles and are schematically illustrated in FIG. 1. This half-track structure 10 includes a track 12 that surrounds a plurality of wheels 14, 16. The two end wheels 14 are mounted directly to the frame with no suspension system. The main load-bearing wheels 16 are individually suspended from the frame.
Other suspension systems are used on vehicles similar to the SNO CAT vehicle, which is made by Tucker Sno Cat Corporation of Oregon, and schematically illustrated in FIG. 2. This half-track structure 20 includes a track 22 surrounding a plurality of wheels 24, 26. The top wheel 24 is connected to a central axle 28. The central axle 28 provides the drive function and is suspended from the vehicle. The remaining wheels 26 are attached to the central axle 28. The track 22 can rotate about the central axle 28, but the central axle links the motion of the two structures 20 on either side of the vehicle.
Finally, there are MUV suspension systems, such as is schematically illustrated in FIG. 3. In this structure 30, a trailing arm 32 is attached to each beam 34 (only one beam shown in the drawing) and connects the beam to a frame (not shown). While each beam may include its own springs or cushions 36, the axles 38 conventionally extend across the vehicle, thereby linking the motion of the two beams.
Such structures are unsatisfactory for use in an off-road setting. Typically, an MUV is used in an area where there are substantial differences in terrain on both sides of the vehicle. It is also desirable to use a half-track on an MUV to permit the MUV to traverse many types of terrain, particularly in wet areas, without sinking. However, no structure has been developed that permits each beam to be independently suspended. In an off-road setting, an independent suspension would be particularly desirable since the variations in the level of the ground can be substantial.
Further, one of the problems to be solved with off-road vehicles is that of travel over large objects, such as logs. Manufacturers have addressed this problem by using low pressure tires. The use of a low pressure tire allows the tire to deform when it encounters an object. This increases the surface area, and hence the friction, between the low pressure tire and the object, enabling the motive force of the vehicle to push the vehicle up and over the object.
However, the use of low pressure tires is not desirable for use with a tracked vehicle. If a low pressure tire is used and the tire deforms, the track tends to have an increased amount of slack at the time of deformation, substantially increasing the risk of the track slipping off the tires. It is inconvenient to attempt to reinstall a track that has become disengaged from the tires, particularly in an off-road setting.
Moreover, if a tracked vehicle is to be used, a high pressure tire should be used to prevent the detachment of the track. Unfortunately, the use of such a tire creates a reduced amount of surface area contact between the vehicle and the obstacle, which causes the track to slip against the obstacle and prevents the vehicle from passing over the obstacle. Therefore, in the prior art a high pressure tire is known to be undesirable.
An additional problem is common among three or more axle vehicles, namely, poor ride performance when a vehicle falls off of an obstacle or step. This problem is illustrated in FIGS. 7 and 8. Only some of the components of the vehicle are illustrated, as it will be apparent to one of ordinary skill in the art how to attach and configure the remaining parts of the vehicle. Turning to FIGS. 7 and 8, a prior art vehicle 40 is shown. The vehicle 40 includes a front wheel 42 attached via a cushion 44 to a front portion of a frame 46. A beam 48 is attached to the rear portion of the frame 46. The beam 48 is supported from the frame 46 by two cushions 44, each of which is near an end of the beam 48. Two wheels 50 are attached to the beam 48. A track (not shown) may be extended around the rear wheels 50. When the vehicle 40 encounters an object 52, such as a log or other object with a steep drop off, the cushion for the front wheel is able to absorb a good bit of the shock with no problem. However, the rear suspension structure does not absorb the shock as well. The rear wheels drop to the ground at the same time and rate as the front wheels, causing the shock to be absorbed by all four rear wheels 50 (two on each side) simultaneously. This shock is quite large, due to the change in damping across all the cushions 44. Accordingly, an improvement is needed to prevent the shock to the system and improved ride conditions.
None of the suspension systems known in the art and described hereinbefore is acceptable for use on an MUV. Specifically, none of the known systems provides an independent suspension for a multi-rear axle vehicle wherein the vehicle is adapted to traverse drop-offs or steps with reduced shock to the vehicle and the occupants. Moreover, none of the known systems provide an independent suspension for a half-tracked vehicle that is adapted to traverse obstacles, such as logs, ruts, and rocks.